Yulia Tymoshenko told The Daily Telegraph that the government was resorting to Stalinist-style tactics and trumped up criminal cases in order to kill off dissent.

"Today's Ukraine is comparable with the USSR in 1937 when innocent people were convicted, jailed, and sometimes sent to their death," she said. "President Viktor Yanukovych is turning a European country of 47 million people into one giant gulag, into a concentration camp."

The darling of Ukraine's 2004 pro-Western Orange Revolution and now the main opposition leader, Mrs Tymoshenko is on trial in a case that many Western observers charge is politically motivated.

Ukrainian prosecutors accused of exceeding her authority as prime minister in 2009 by brokering a gas deal with Russia that lost £118 million.

If found guilty, she faces up to a decade in jail and would be disqualified from taking part in parliamentary elections next year and a presidential poll in 2015.

If that was not enough, she is facing a string of other criminal charges too, all of which she insists are fabricated.

Several of her former cabinet ministers have also been targeted in police investigations. The former interior minister is languishing in jail, while her economy minister has won political asylum in the Czech Republic after being hounded by the authorities. She herself is not allowed to travel abroad or even leave the city limits of Kiev, the Ukrainian capital, for the duration of her trial.

"I am at peace with myself as I have done nothing to deserve such punishment," Mrs Tymoshenko said. "I did not break the law and I have done nothing that could be associated with corruption."

Sat near a framed photograph of her and Baroness Thatcher and religious icons, the 50-year-old politician said that she thought her persecution was personal.

President Yanukovych, an apparatchik who she referred to as "a Neanderthal," had decided to go all out to remove her and her supporters from the political arena, she claimed.

"He thinks he lives in the former USSR behind the Iron Curtain and that he can do what he wants," she said. "He wants to liquidate the opposition and remove me as a rival by putting me in jail so that he can stay in power. It is the recipe that the KGB used."

Since coming to power last year, Mr Yanukovych, a former mechanic, has strengthened his own presidential powers, signed a deal that allows Russia's Black Sea Fleet to remain in Ukraine until 2042, and boosted the use of the Russian language in everyday life.

In the process, critics contend he has clamped down on opposition media, stifled meaningful opposition, and turned the former Soviet republic into a pale imitation of the USSR circa 1970 when Leonid Brezhnev was in power.

Mr Yanukovych rejects that, saying he has brought much-needed stability and repaired badly damaged relations with Ukraine's biggest neighbour: Russia. He has also denied any involvement in Mrs Tymoshenko's trial. The trial, which has been disrupted by brawling among her supporters and government backers as well as the hospitalisation of her own lawyer, represents a dramatic reversal of fortune for someone who has twice served as Ukraine's prime minister and only last year narrowly lost a presidential election.

Famed for her love of sharp designer suits and a trademark peasant-style hair braid, Mrs Tymoshenko admitted she was in a difficult situation. But she said she was not letting herself be overcome by fear or despair. "It is unpleasant and any normal person would want to run away but I am not frightened."

People close to President Yanukovych have suggested she flee to a country of her choice, she added. "But I will never give them that pleasure," she smiled, fighting to hold back the tears.

Mrs Tymoshenko is said to have made a fortune in the aftermath of the 1991 collapse of the Soviet Union in the gas industry and is no stranger to the vicious nature of Ukrainian politics. In 2001, during a political standoff with Ukraine's then president, she was thrown in jail for 42 days before eventually being exonerated by the supreme court.

Clearly still troubled by the memories of that ordeal, she said she ignored multiple threats at the time to stop battling corruption, and made it clear she would not be intimidated into stepping aside this time either.

"Back then I was warned that if I did not stop harsh measures would be taken against me. They then threw my husband in jail and told me to stop if I did not want to be next. I did not stop so they threw me in jail too. I have already been through one round of political repression. It was very tough but I can take a second round."

A strong believer in God and a member of the Ukrainian Orthodox Church, she said her conscience was clear. "There is a higher court than President Yanukovych," she said without a smile looking upwards.